This invention relates to an electro-optic device for altering the density of charge carriers within an integrated optical waveguide. Such a device may be used as an attenuator or in applications which make use of the change in refractive index caused by the charge carriers, e.g. as a phase modulator in a Mach-Zehnder interferometer.
It is known to form an attenuator or phase modulator in the form of a lateral p-i-n diode across an integrated optical waveguide. Examples of such devices are described in U.S. Pat. No. 5,755,986, GB2333851A and WO00/10039, the disclosures of which are incorporated herein. Such devices may be also be used in a wide variety of other applications.
The present invention aims to provide an improvement of such devices.
According to a first aspect of the invention, there is provided an electro-optic device comprising a substrate, an integrated optical waveguide extending across the substrate, and means arranged to apply an electrical signal across the waveguide via two doped regions to alter the attenuation properties and/or the refractive index of the waveguide by altering the density of charge carriers within the waveguide, the two doped regions each comprising a plurality of doped areas spaced apart from each other in a direction parallel to the length of the waveguide the size and spacing of the doped areas being selected so that the efficiency of the device, in terms of the increase in attenuation or change in refractive index per unit current applied thereto, is increased.
According to a second aspect of the invention, there is provided an electro-optic device comprising a substrate and an integrated optical waveguide extending across the substrate, wherein the waveguide comprises a series of two or more curved portions curving in alternating directions, each having an n-doped region adjacent the outer side of the curved portions and a p-doped region on the inner side thereof so as to form a series of diodes of alternating polarity along the length of the waveguide.
This second aspect of the invention enables a diode to be formed in a curved portion of a waveguide, which may be used in conjunction with the first aspect of the invention.
Preferred and optional features of the invention will be apparent from the following description and from the subsidiary claims of the specification.